1. Field of the Invention
This invention relates to new methods of treating the surface of rubber and rubber-based materials to improve their ability to be bonded to other materials. For example, to improve their ability to be bonded to any type of adhesive (including sealants) and, matrix materials including, but not limited to, thermoset or thermoplastic polymers and inorganic matrices.
2. Description of Related Art
By the term "rubber" as used here in the description and claims we mean any natural or synthetic rubbers, their mixtures and/or their blends and/or their alloys with polymers. Examples of suitable rubbers and rubber based materials for use in the invention include, but are not limited to, natural rubber, ethylene-propylene diene rubber, synthetic cis-polyisoprene, butyl rubber, nitrile rubber, copolymers of 1,3-butadiene with other monomers, for example styrene, acrylonitrile, isobutylene or methyl methacrylate, and ethylene-propylene-diene terpolymer. While it is preferred that the rubber be vulcanised, the composition of the present invention can also be formed using virgin or devulcanised rubber. The term "vulcanised rubber" as used herein includes vulcanised rubbers and vulcanised rubbers bound with fillers, additives, and the like. Examples, of filler and additives include carbon black, silica, fiber, oils, and zinc oxide.
In a preferred application of the invention, it is desirable to form a strong and durable adhesive bond between a rubber or rubber based material in the form of flat sheet, film, woven fabric, fiber, web or particulate and adhesive and other polymeric binder and/or matrix material or non-polymeric binder or matrix materials.
In order for the adhesive bond or composite material to perform satisfactorily, there must be good adhesion between the rubber or rubber material (e.g. flat sheet, fiber, or particulate) and the adhesive or the matrix (e.g. thermoplastic or thermoset polymers or non-polymeric materials). Preferably the halogenating agent is selected from the group consisting of aqueous or organic solvent-based chlorine, iodine, and bromine solutions and acidified hypochlorite solutions. However, it is well known that many vulcanised natural or synthetic rubbers and/or their mixtures with polymers are difficult to bond due to the absence of specific surface functional groups and/or molecular structure capable of providing reactive sites for strong interfacial interactions such as mechanical entanglement, acid-base interactions, and/or the formation of chemical bonding (e.g. covalent or ionic, etc) between the untreated substrate and the adhesive or matrix material.
Typical surface treatments for enhanced adhesion of rubbers and rubber-based materials include: mechanical abrasion; corona discharge, plasma treatment, photo-chemical treatment, and surface halogenation with the use of free halogen in aqueous or organic solutions or in gaseous phase, and/or inorganic and organic halogenating agents.
In the prior art halogenating agents are used in solutions at concentrations of 0.5 to 5% per weight, preferably at 1 to 3%. In order for the solution of the halogenating agent to be effective, its concentration should be greater than 0.5%, otherwise the adhesion enhancement is insignificant. At lower concentrations, i.e. below 0.5% the solutions of halogenating agents in known applications are ineffective due to the lack of sufficient interfacial chemical activity between the rubber surface and the active species in the solution.